The present invention relates to a distance detecting apparatus for optically measuring the distance from a vehicle to an object such as an obstacle, a preceding vehicle, etc., lying ahead thereof.
Some typical examples of such a distance detecting apparatus are disclosed in Japanese Patent Publication Nos. 63-38085 and 63-46363. The apparatuses disclosed therein commonly have a pair of first and second parallel optical systems having two convex lenses 101, 102 disposed in a horizontally aligned relation at a prescribed distance L away from each other, as shown in FIG. 5. A pair of separate image sensors 103, 104 are horizontally disposed at focal points of the lenses 101, 102 apart their focal distance f from the locations of corresponding lenses 101, 102, respectively, for generating respective image signals to a common signal processor 120. The signal processor 120 successively shifts the image signals from the image sensors 103, 104 and electrically superposes them one over the other, so that the perpendicular distance R from the lenses 101, 102 to an object 121 is calculated based on the principle of triangulation using the following formula: EQU R=(f.times.L)/d
where d is a shift distance by which the image signals are moved to obtain the best match.
With the above-described conventional distance detecting apparatus as constructed above, however, if there are many objects within the field of view of the image sensors 103, 104, it is unclear to which object the distance from the subject vehicle is being detected. In particular, let us assume that the distance to an object in the form of a preceding vehicle is detected by the above-described distance detecting apparatus mounted on the subject vehicle during the travel thereof. In this, case, if another vehicle travelling on a lane of a road adjacent the one on which the subject vehicle is travelling comes into the field of view of the subject vehicle, it is not clear at all or the driver cannot tell to which vehicle (i.e., travelling on the same lane or on an adjacent lane) the distance is detected.